Root New Atrix 4G help needed

[JustaCrow]

Hi all. I just bought an Atrix 4G. I used to have AT&T but have now switched to Straight Talk. I am having problems switching my "APN" to Straight Talk. I have 5 "APN"s 4 are AT&T, and one is Straight Talk. I cannot delete the AT&T ones, nor can I make the phone use the Straight Talk one. What am I doing wrong?

Thanks!